Question

An iron gate rusts within a short span of time but the iron pillar in the
Qutub minar Complex has not rusted even after more than 1600 years.
Why do you think it is so?​

Answer 1

The Iron Pillar in Qutub Minar has not rusted because:

It was casted using best techniques of metallurgy. They used block technique of casting. Where pillar was casted block by block. There by removing maximum number of impurities. Pillar's resistance to corrosion is due to a passive protection film at the iron rust surface. The presence of slag and unreduced iron oxides in the micro structure of iron, high amount of phosphorus in metal and the alternate drying and wetting under atmospheric conditions are the three main factors in the formation of protective passive welding.

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Answer 2

Answer:

The corrosion resistance of the iron pillar results from an even layer of crystalline iron(III) hydrogen phosphate hydrate forming on the high-phosphorus-content iron